Because intrinsic electrochemical properties of materials are greatly influenced by electron transfer and distribution therein, it is very important to simulate the behavior of an electron in a molecule in developing a material. The behavior of an electron is expressed as the probability of finding an electron in any specific region in a molecular. A molecular orbital is introduced as a concept to simulate the behavior of an electron. A molecular orbital, which accounts for the distribution of an electron in a specific region in a molecular structure as a probability concept, cannot be obtained experimentally, but can be constructed by the Schrödinger equation using quantum mechanics.
The molecular orbital distribution that has been quantum-mechanically computed thus far is regarded as a qualitative measurement in which 3- or 2-dimensional diagrams created through a contour plot are used for visual comparison, for example, as described in “Analysis of Electron Delocalization in Aromatic Systems: Individual Molecular Orbital Contributions to Para-Delocalization Indexes (PDI)”. FIG. 1 is a diagram showing the molecular orbital distribution of NPB (N,N′-Di[(1-naphthyl)-N,N′-diphenyl]-1,1′-(biphenyl)-4,4′-diamine), which is used in an OLED film, in terms of Neutral/HOMO. To depict FIG. 1, Materials Visualizer of the program Materials Studio for simulating and modeling molecular orbitals was used. In the diagram, the molecular orbital distribution is expressed as a region in which an electron is likely to exist (yellow/green regions). FIG. 1 shows a generally even molecular orbital distribution over the entire molecule.
As is perceived in this case, however, the qualitative measurement through visualization does not provide an accurate criterion of analysis, so that even the same molecular orbital distribution may be analyzed differently. For FIG. 1, by way of example, there may be different estimation results: (1) the molecular orbital is highly evenly distributed because the molecular orbital is distributed over the entire molecule, or (2) the molecular orbital is fairly distributed because the distribution is poor in opposite ends of the naphthalene moieties. The problem with this qualitative measurement is more evident when two molecular orbital distributions, rather than one molecule, are compared to each other. In many materials development cases, electrochemical properties are estimated by comparing the distribution of molecular orbital A with that of molecular orbital B. Since the qualitative comparison through visualization may result in greatly different estimation data depending on the criterion, estimation of two or more molecular orbital distributions is more prone to being inaccurate than that of one molecular orbital distribution. This problem does not arise only upon the comparison of molecular orbital distributions, but is one of the most fundamental limits for all qualitative approaches. Given an effective, accurate and reliable measurement approach to the molecular orbital distribution, which has been estimated only qualitatively thus far, materials development can be more effectively achieved with reference to properties determined by the molecular orbital distribution as well as the fundamental properties determined by electron transfer, such as electron affinity.
In this regard, Japanese Patent Application Unexamined Publication No. 2011-173821 discloses a novel method for predicting the activity of a new chemical material using an index of reactivity of a molecule, computed on the basis of quantum chemistry calculation in consideration of a reactive molecular orbital as well as a frontier orbital. However, this conventional method is limitedly applied to the quantitative comparison of molecular orbital distributions between two molecules.
To overcome the limitation of conventional qualitative methods, the present inventors developed the novel method MOD-Dscore by which molecular orbital distribution profiles can be quantitatively estimated. Configured to have a value between 0.0 and 1.0, the system established by the MOD-Dscore method further approaches to 1.0 for a more identical orbital distribution between two molecules, and is farther away from 1.0 for greater difference in molecular orbital distribution between two molecules. MOD-Dscore allows for the expression of a difference in molecular orbital distribution between two molecules as a digitized value, thereby accurately estimating molecular orbital distributions in a quantitative manner.
For instance, assume that molecules A1, A2, and A3 are calculated to have MOD-Dscore values of 0.995, 0.875, and 0.893, respectively, with regard to molecule A over the entire structure of which a molecular orbital is evenly distributed. The molecular orbital distribution of A1 is regarded as being similar to that of A because its MOD-Dscore value is 0.995, which approximates to 1.0 whereas A2 and A3 are estimated to be different in molecular orbital distribution from A because their MOD-Dscore values are significantly smaller than 1.0. As such, MOD-Dscore computation can reveal that the molecular orbitals are not evenly distributed over the entire molecules of A2 and A3; however, it cannot explain the regions where the molecular orbitals of A2 and A3 are localized, which makes A2 and A3 different in molecular orbital properties from A. There is now a need for a novel approach to assessing a region where a molecular orbital is localized. In this context, first, the present inventors construct a region specific-molecular orbital library (R-MO library), which can be used as a reference in assessing molecular orbital distributing regions. Constructed with molecular orbital distributions of materials having specific structure regions, the R-MO library can be used as a reference in estimating molecular orbital distributing regions, and there is also a need for extending the R-MO library.